Tactile measuring methods in which surfaces are probed by mechanical probing elements and can be measured very precisely have become established for precise measurement of shafts. However, tactile measuring methods generally require extensive changeover times when changing measuring tasks.
In such cases, optical measuring methods are available. These optical measuring methods generate a shadow image of the shaft by which the outer contour can be measured. Owing to the noncontacting measurement, the machine element can be determined faster and measured with high accuracy. It is possible to alternate easily and quickly between different measuring tasks. A disadvantage of optical measuring devices is that concave surface portions and undercuts, for example, which are not visible in the shadow image cannot be measured.
For these reasons, an optical measuring method and a tactile measuring method can be combined in one device. Patent DE 103 19 947 B4 discloses a device in which circumferential surfaces of shafts are detected by combined application of optical and mechanical measuring units. To this end, the device has a measuring system in which a mechanical-electrical measuring unit is integrated in an optoelectronic measuring unit for measuring the shaft and can be moved out linearly if required. In so doing, a shaft is clamped in the device on the axis of rotation of the shaft. The measuring system has a U-shaped optoelectronic measuring unit whose cantilevering ends are arranged on both sides of the clamped shaft in a first measuring position. Illumination/camera modules operating in the manner of a light barrier are installed in the cantilevering ends. In this way, a shadow image of the shaft is generated and recorded in a known manner, and this shadow image can be used for measuring the shaft. In order to detect the shaft in its entirety, the shaft is rotated around its rotational axis and the optoelectronic measuring unit is moved along the shaft parallel to the axis of rotation. To heighten measuring accuracy, an additional measurement of the circumferential surfaces of the shaft can then be carried out by the mechanical-electrical measuring unit which is fastened to the base of the U-shaped optoelectronic measuring unit. Along with the movement of the optoelectronic measuring unit, the mechanical-electrical measuring unit is also guided along the shaft automatically so that the circumferential surfaces can be mechanically probed in this second measuring position. In so doing, reception of measurement values takes place perpendicular to the axis of rotation of the shaft within the axial plane so that the circumferential surfaces can be detected tactilely with high accuracy by the probing element. However, it allows accurate mechanical probing of circumferential surfaces exclusively. Surfaces disposed substantially orthogonal to the axis of rotation of the shaft can only be detected optically. In view of the fact that mechanically stable and, therefore, solid component parts are employed as a rule in order to maintain a high measuring accuracy of the device, it must be assumed that increased constructional expenditure is required to realize a precise displacement of the movably mounted U-shaped support between the two measuring positions.